面试经典150题——Day34

一、题目

36. Valid Sudoku

Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

Each row must contain the digits 1-9 without repetition.
Each column must contain the digits 1-9 without repetition.
Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.
Note:

A Sudoku board (partially filled) could be valid but is not necessarily solvable.
Only the filled cells need to be validated according to the mentioned rules.

Example 1:

Input: board =
[[“5”,“3”,“.”,“.”,“7”,“.”,“.”,“.”,“.”]
,[“6”,“.”,“.”,“1”,“9”,“5”,“.”,“.”,“.”]
,[“.”,“9”,“8”,“.”,“.”,“.”,“.”,“6”,“.”]
,[“8”,“.”,“.”,“.”,“6”,“.”,“.”,“.”,“3”]
,[“4”,“.”,“.”,“8”,“.”,“3”,“.”,“.”,“1”]
,[“7”,“.”,“.”,“.”,“2”,“.”,“.”,“.”,“6”]
,[“.”,“6”,“.”,“.”,“.”,“.”,“2”,“8”,“.”]
,[“.”,“.”,“.”,“4”,“1”,“9”,“.”,“.”,“5”]
,[“.”,“.”,“.”,“.”,“8”,“.”,“.”,“7”,“9”]]
Output: true
Example 2:

Input: board =
[[“8”,“3”,“.”,“.”,“7”,“.”,“.”,“.”,“.”]
,[“6”,“.”,“.”,“1”,“9”,“5”,“.”,“.”,“.”]
,[“.”,“9”,“8”,“.”,“.”,“.”,“.”,“6”,“.”]
,[“8”,“.”,“.”,“.”,“6”,“.”,“.”,“.”,“3”]
,[“4”,“.”,“.”,“8”,“.”,“3”,“.”,“.”,“1”]
,[“7”,“.”,“.”,“.”,“2”,“.”,“.”,“.”,“6”]
,[“.”,“6”,“.”,“.”,“.”,“.”,“2”,“8”,“.”]
,[“.”,“.”,“.”,“4”,“1”,“9”,“.”,“.”,“5”]
,[“.”,“.”,“.”,“.”,“8”,“.”,“.”,“7”,“9”]]
Output: false
Explanation: Same as Example 1, except with the 5 in the top left corner being modified to 8. Since there are two 8’s in the top left 3x3 sub-box, it is invalid.

Constraints:

board.length == 9
board[i].length == 9
board[i][j] is a digit 1-9 or ‘.’.

题目来源： leetcode

二、题解

我自己的笨方法

class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        unordered_map<char,int> map;
        //遍历行
        for(int i = 0;i < 9;i++){
            //清除上行数据
            map.clear();
            for(int j = 0;j < 9;j++){
                char c = board[i][j];
                if(c != '.'){
                    if(map[c] == 0) map[c]++;
                    else if(map[c] == 1) return false;
                }
            }
        }
        //遍历列
        for(int j = 0;j < 9;j++){
            map.clear();
            for(int i = 0;i < 9;i++){
                char c = board[i][j];
                if(c != '.'){
                    if(map[c] == 0) map[c]++;
                    else if(map[c] == 1) return false;
                }
            }
        }
        //遍历3x3宫格
        for(int i = 0;i < 9;i += 3){
            for(int j = 0;j < 9;j += 3){
                map.clear();
                for(int k = i;k < i + 3;k++){
                    for(int m = j;m < j + 3;m++){
                        char c = board[k][m];
                        if(c != '.'){
                            if(map[c] == 0) map[c]++;
                            else if(map[c] == 1) return false;
                        }
                    }
                }
            }
        }
        return true;
    }
};

答案的好方法

class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        int rows[9][9];
        int columns[9][9];
        int subboxes[3][3][9];
        
        memset(rows,0,sizeof(rows));
        memset(columns,0,sizeof(columns));
        memset(subboxes,0,sizeof(subboxes));
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                char c = board[i][j];
                if (c != '.') {
                    int index = c - '0' - 1;
                    rows[i][index]++;
                    columns[j][index]++;
                    subboxes[i / 3][j / 3][index]++;
                    if (rows[i][index] > 1 || columns[j][index] > 1 || subboxes[i / 3][j / 3][index] > 1) {
                        return false;
                    }
                }
            }
        }
        return true;
    }
};